The government's flagship Help to Buy mortgage guarantee scheme has united economists in condemnation, according to one leading expert.

Jonathan Portes, director at the National Institute of Economic and Social Research and former chief economist at the Department for Work and Pensions, told delegates at the Chartered Institute of Housing conference that the £12bn scheme would inflate house prices without boosting supply.

"Help to Buy has one real achievement, which is often thought to be impossible," he said. "It has managed to unite every single economist I know.

"It is a policy which has managed to unite the entire economics profession in condemnation as a policy which is likely to push up demand while achieving virtually nothing on supply. It is a backhanded compliment to the government to say they have managed to achieve this."

The multi-billion pound scheme, which was a key part of George Osborne's budget announcement earlier this year, offers buyers a government equity loan of up to 20% of a property's value so a property can be purchased with just a 5% deposit. A further £12bn mortgage guarantee scheme will be available to mortgage lenders from January 2014.

However, Peter Schofield, director general of neighbourhoods at the Department for Communities and Local Government, defended the scheme.

"The Help to Buy equity loan scheme has been a huge and immediate success," he said, "With over 4,300 reservations in the first two months of the scheme, and developers saying they plan to build about 10% more each year to meet this growth in demand."

Andy Rose, chief executive of the Homes and Communities Agency, also backed the scheme, saying it was working "incredibly well".

"If you look at housebuilders' announcements and quarterly results, a lot are giving recognition to Help to Buy for stimulating the market for new homes, which was what it was set up to do," he said.

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